Google Inc is opening its much-anticipated Chrome software to external developers, as the search giant prepares to expand its reach into operating systems.

The company hosted a media event on Thursday to show off the free cloud-based software, which it hopes to have on the market in netbooks ahead of the 2010 holiday season. Google executives said they designed Chrome with an emphasis on speed, security and simplicity.

The software currently starts up on a PC in seven seconds, and Google said it is hoping to cut the boot time further.

But the company said Chrome at least initially will not be able to run on just any PC, and it plans to specify certain hardware requirements to run the software, such as solid-state hard drives.